Objects fabricated from a highly glossy material, such as specular objects or mirror-like objects, have reflection characteristics that differ significantly from those fabricated from a diffuse material. For example, whereas for a diffuse material light from a directional light source such as a projector is reflected in virtually all directions, for a highly glossy material, such light is reflected in primarily only one direction or at most only a few directions. These reflections are called “specular” reflections, and are caused by the shiny surface of the glossy material, which often has a mirror-like surface finish. As a result, an image of a highly glossy object illuminated by a directional light source is often completely dark, unless the camera happens to be positioned at the precisely correct viewing direction so as to capture the specular reflection.
For these and other reasons, conventional 3D scanning methods that work well with diffuse objects, such as projection of images of structured light onto the surface of the object, or photometric stereo, do not work well with specular or highly glossy objects.